Have you figured in the space that the tent hinge needs to open? It’s got to be designed that way for that I bet.
What you want is this: https://www.frontrunneroutfitters.com/en/us/universal-track-non-drilled-1800mm-l.html They have other lengths available, too. I have personally used this product and it is very strong.
Unistrut. Use the thinner one and eliminate the second cross bar that channel is sitting on too.
Help me out here. There are LOTS of unistrt parts etc. What do you mean remove the other cross bars?